#Read  keyboard the First number 
first=int(raw_input('Introduce the FIRST NUMBER:'))
#Read keyboard the Final number 
final=int(raw_input('Introduce the FINAL NUMBER:'))
#Compare the first number with Final number because 
#Initial number must be less than the final number
if (first < final and first > 0 and final > 0) :
    i=first
    sum=0
    #We use the for statement to sum the numbers between these two intervals    
    for i in range (first,final+1):
        #sum to number final        
        sum = sum + i
    #Print result
    print(sum)
else :
     print 'Initial number can not be greater than the final number'